Mitt Romney’s financial company, Bain Capital, invested in a series of firms that specialized in relocating jobs done by American workers to new facilities in low-wage countries like China and India.

During the nearly 15 years that Romney was actively involved in running Bain, a private equity firm that he founded, it owned companies that were pioneers in the practice of shipping work from the United States to overseas call centers and factories making computer components, according to filings with the Securities and Exchange Commission.

While economists debate whether the massive outsourcing of American jobs over the last generation was inevitable, Romney in recent months has lamented the toll it’s taken on the U.S. economy. He has repeatedly pledged he would protect American employment by getting tough on China.

“They’ve been able to put American businesses out of business and kill American jobs,” he told workers at a Toledo fence factory in February. “If I’m president of the United States, that’s going to end.”

Speaking at a metalworking factory in Cincinnati last week, Romney cited his experience as a businessman, saying he knows what it would take to bring employers back to the United States. “For me it’s all about good jobs for the American people and a bright and prosperous future,” he said.

For years, Romney’s political opponents have tried to tie him to the practice of outsourcing American jobs. These political attacks have often focused on Bain’s involvement in specific business deals that resulted in job losses.

But a Washington Post examination of securities filings shows the extent of Bain’s investment in firms that specialized in helping other companies move or expand operations overseas. While Bain was not the largest player in the outsourcing field, the private equity firm was involved early on, at a time when the departure of jobs from the United States was beginning to accelerate and new companies were emerging as handmaidens to this outflow of employment.

Bain played several roles in helping these outsourcing companies, such as investing venture capital so they could grow and providing management and strategic business advice as they navigated this rapidly developing field.

Over the past two decades, American companies have dramatically expanded their overseas operations and supply networks, especially in Asia, while shrinking their workforces at home. McKinsey Global Institute estimated in 2006 that $18.4 billion in global information technology work and $11.4 billion in business-process services have been moved abroad.